[Biology Class Notes] on Stomata Pdf for Exam

The most basic function that plants exercise in order to stay alive is photosynthesis. This is the process through which plants utilize sunlight, carbon dioxide and water to generate oxygen and synthesize food for themselves. Now, this process is a complex network of many different processes working together. This would not be possible without the presence of stomata in plants. 

Stomata refer to the pores that are present, usually on the underside of leaves of a plant, which allow for the exchange of the gases oxygen and carbon dioxide. In very simple terms, it can be said that stomata enable the plant to breathe, just as the nose in humans allows them to breathe. 

Stomata Definition

When examined under a microscope, we observe multiple tiny pores located in proximity to a leaf. These pores are collectively called stomata; a single pore is called Stoma. This is the stomata meaning that you must know. These minute openings are generally located in the epidermis layer of leaves; however, they can be found on other parts of a plant like a stem. Stomata facilitate the movement of gasses like oxygen and carbon dioxide, which are essential for photosynthesis.

Types of Stomata 

Stomata are classified based on the strength of their cluster and the subsidiary cells that surround them:

Commonly known as the irregular-celled type or ranunculaceous cells, Anomocytic stomata are surrounded by cells that are not much different from other epidermal layers as far as their size and shape are concerned. A Stoma is not surrounded by a definite number or arrangement of cells; it appears to be embedded in the epidermal cells.

An Anisocytic Stomata is surrounded by three lopsided subsidiary cells, where one is distinctly smaller than the other two; Anisocytic stomata is also known as cruciferous or unequal celled type stomata.

Also called parallel-celled type or rubiaceous cells, Paracytic Stomata are accompanied on each side by one or more subsidiary cells; the longitudinal axes of these subsidiary cells lie parallel to the aperture of the guard cells.

A pair of subsidiary cells surround Diacytic stomata; the walls of these subsidiary cells lie at right angles to the guard cells; They are also called caryophyllaceous or cross-walled stomata.

Gramineous stomata possess two guard cells shaped like dumbbells; each guard cell consists of a narrow middle portion and two bulbous ends. The narrow central part is sturdy and thickened; the subsidiary cells are parallel to the long axis of the pore.

What is the Structure of Stomata?

The stomata are made up of minute pores called Stomata, which are surrounded by guard’s cells. A Stoma exhibits turgor pressure; they swell and become rigid upon absorption of fluids; with this characteristic’s help, the cells operate by opening and closing according to the turgidity of the guard cells. However, the cell wall surrounding the Stoma tends to be robust, flexible, and thinner; how the guard cells are shaped differs in both dicots and monocots, but the mechanism remains the same. 

These small openings are usually seen in the epidermis layer of the leaves in the plant and also in other parts of the plant, such as the stem. Basically, any part of the plant that is green in colour contains stomata. Stomata help to diffuse gases such as oxygen and carbon dioxide. 

A Stoma’s Structure is Made of the Following:

It’s the outermost layer of a plant made up of specialized cells that originate from the dermal tissues; Epidermal cells tend to be irregular in shape, and their function is to provide mechanical support to the plant.

Located adjacent to guard cells in the Stroma of a leaf, subsidiary cells provide support, which helps in the movement of guard cells; subsidiary cells are generally formed in proximity to mother cells. However, they can be seen growing independently too.

They refer to the minute pores or the openings found under the surface of a leaf; these pores play a significant role in the exchange of gases like oxygen and carbon dioxide.

These cells resemble the shape of a kidney or dumbbell-shaped, and its primary function is to properly carry out the opening and closing mechanism of the Stoma.

What is the Purpose of Stomata?

Diffusion of gases is the main function that stomata undertake. The guard cells help with this function by opening and closing at the required time to exchange gases. It should be mentioned here that the process of gas and water exchange that is performed here is known as transpiration. When plants take in the air, they use the carbon atoms to make their food and reserve it for energy, while the oxygen then gets bonded with hydrogen and gets diffused into the atmosphere. This is the reason why plant surfaces such as leaves often have water droplets on them. 

Water is required for the plant to produce energy for food. This is done by the roots, which absorb water from the soil through osmotic pressure. Water moves to wherever the concentration of ions, atoms, and molecules is the highest. This osmotic pressure makes the guard cells of the stomata open and close. 

Other than this, stomata play a very deterministic role in photosynthesis as well.